1. Field of the Invention
The invention relates to the field of optical power regulators for fiber optic network, and particularly to a dual fiber variable optical attenuator.
2. The Related Art
A fiber optical attenuator is an optical component that is intended to control the optical power propagating in the fiber. Optical attenuators are widely used in the optical transmission system and the optical network, and especially in the optical wavelength division multiplexing (WDM) network. The motor driven optical variable attenuator is a new kind of related device used in the WDM network.
U.S. Pat. No. 5,745,634 discloses a costly design using two lens for optical coupling and using a normal DC motor to control the motion.
Differently, the copending application Ser. No. 09/174,367 having the same assigned with the instant application, discloses a systematic design where a neutral density (ND) filter is placed between two collimators, and a step motor is employed to electrically control the position of the ND filter for obtaining the specific attenuation value. Under this situation, the input and the out put fibers are respectively positioned on two sides of the whole package box.
As noted, in the WDM optical network system arrangement, it is preferred to have the input fiber and the corresponding output fiber extend on the same side for compact size consideration. Thus, the copending application Ser. No. 09/255,915 also having the same assignee with the instant application, demonstrates the architecture of duel fiber collimator optical variable attenuator, where both the input fiber and the output fiber are located on one side of the whole package.
Anyhow, it is noted because in the copending 09/255,915 design, the reflection of the light occurs on the ND fiber which is actuated/controlled by the step motor. In practice, this type of design may create attenuation instability due to relatively great tolerance/oscillation of the motor motion which results in the inferior reflection effect.
Therefore, an object of the invention is to provide a variable optical attenuator not only with a compact size but also very good reliability performance being not influenced by the motion of the step motor.
According to an aspect of the invention, a variable optical attenuator comprises a dual fiber collimator and a reflecting component separated by a linearly moveable ND filter wherein said ND filter is either manually controlled or electrically controlled by a step motor.
Another feature of the invention provides significant spacing between the GRIN lens and the reflecting component (such as a mirror) to place the ND filter in between.
Another feature of the invention provides spacing between the ND filter and the reflecting component to have the focal point of the GRIN lens located on the reflecting component.
Another feature of the invention provides a lateral offset between the axis of the ferrule, a mechanical part, and that of the GRIN lens so as to efficiently capture the reflected light from the reflecting component and the ND filter.